The present invention relates to a fire damper used in an air duct system, and more particularly, to a damper having a shutter plate or flap which rotates to shut the duct when temperature of air flowing through the duct rises to a predetermined height.
There has been known a fire damper employing a temperature fuse as a temperature detecting and actuating element. Generally, such conventional fire damper has a tubular casing to be inserted in a middle way of an air duct of an air ventilation system or the like, a flap provided in the casing in a rotatable manner about an axis extending in the diameter direction of the casing, a spring urging the flap to rotate in a direction to shut the duct, and a trigger member or a stopper mechanism made of a temperature fuse to keep the flap in a rotated state by substantially right angle against urging force of the spring.
And when fire happens, the fuse melts and the flap is rotated by the spring to close the passage of the duct.
However, such conventional type of fire damper has drawbacks that several length of fuses must be prepared for various diameters or widths of ducts, since the fuse is stretched between a lateral periphery of the flap and the inside surface of the duct so as to extend in a radial direction of the duct. In addition, temperature detecting function based on the melting point of the fuse is not stable, and actuating speed based on the melting speed of the fuse is comparatively slow.
In order to improve the temperature detecting function and actuating speed, it has been proposed to employ a coil spring made of form memory alloy, for example, Ti-Ni, Cu-Zn, In-Tl or the like, as a temperature detecting and actuating element. Such fire dampers are disclosed in Japanese Unexamined Utility Model Publications No. 103156/1986 by Sharp Kabushiki Kaisha and No. 59659/1988 by Kabushiki Kaisha Daito Kosakusho who is assignee of the instant application.
The former fire damper has a stopper pin inserted through a hole in a wall of a casing and engaged with a lever fixed to an end of a rotary shaft of a flap. The spopper pin is urged in a disengageable direction by a compression spring, and is ordinary stopped in its engaging state by a somewhat complex trigger mechanism including a coil spring made of form memory alloy. The spring made of form memory alloy has plasticity at a temperature under the metamorphosis point and bacomes to have elasticity at a temperature higher than the metamorphosis point, and then the spring behaves as a compressin spring.
The latter fire damper has another trigger mechanism comprising a trigger lever rotatably supported with a bracket fixed to a duct wall, a tubular member coaxially fixed with a rotary shaft of flap and has a slit engageable with the trigger lever, and a coil spring made of form memory alloy which behaves as a tension spring under heating.
In the proposed fire damper, the trigger lever is generally engaged with the tubuler member to stop the rotation of the flap, and when fire happens the form memory alloy spring rotates the trigger lever to allow rotation of the flap.
Those coil spring made of form memory alloy is sensitive to change of temperature for a special temperature in accordance with the kind of alloy, i.e. for the transform point or metamorphosis point of the alloy, and the shrinking speed is very quick when the temperature changes across the metamorphosis point.
However, the damper has a lot of parts, especially a lot of movable elements, and therefore, the structure is very complex. As a result, breakdown often happens in the damper, and the superior functions of the form memory alloy is not efficiently utilized.
An object of the present invention is to provide a fire damper in which the member of parts is not large so that breakdowns happens less, temperature detecting and actuating function is good, and can be employed in various sizes of ducts.